Sulfur cured rubber that contains one or more reinforcing fillers is utilized in manufacturing a wide variety of products that require high strength and abrasion resistance, such as tires. For instance, carbon black and synthetic amorphous silica, such as precipitated silica, are commonly used as reinforcing fillers in tires, power transmission belts, conveyor belts, hoses, and a wide variety of other articles of manufacture.
Silica is normally used as a filler for rubbery polymers in conjunction with a silica coupling agent in order to aid in coupling the silica to the elastomer, such as natural or synthetic rubber. Such silica coupling agents typically contain a moiety which is reactive with the hydroxyl groups present on the surface of the silica, such as silanol groups, and another moiety which is interactive with the elastomer being reinforced.
The moiety of the silica coupling agent that reacts with the hydroxyl groups on the surface of the silica is normally a silane-based moiety such as an alkoxysilane group. Bis (3-ethoxysilylpropyl)polysulfide is a representative example of a typical silica coupling agent that contains from 2 to about 6 connecting sulfur atoms in its polysulfidic bridge (average of about 2 to about 2.6 connecting sulfur atoms in its polysulfidic bridge). The interaction of such silica coupling agents with hydroxyl groups on the surface of the silica generates an alcohol, such as ethanol, and water as reaction byproducts.
U.S. Pat. No. 6,417,286 discloses a method of processing a rubber composition which comprises mixing (i) 100 parts by weight of at least one sulfur vulcanizable elastomer selected from conjugated diene homopolymers and copolymers and from copolymers of at least one conjugated diene and aromatic vinyl compound; and (ii) 0.05 to 10 phr of an titanium or zirconium compound of the formula (R1—O)y—X—(O—R2—W)z wherein each R1 is independently selected from the group consisting of alkyl radicals having from 1 to 8 carbon atoms; R2 is a divalent radical selected from the group consisting of alkylenes having 1 to 15 carbon atoms, arylene and alkyl substituted arylene groups having 6 to 10 carbon atoms; W is an epoxy group; and y is an integer of from 1 to 3, z is an integer of from 1 to 3 and the sum of y and z equals 4; and X is titanium or zirconium.
U.S. Pat. No. 6,809,135 discloses a tire having a component of a rubber composition which comprises (A) elastomer(s) consisting of 100 parts by weight of at least one diene-based elastomer selected from homopolymers and copolymers of isoprene and/or 1,3-butadiene and copolymers of at least one of isoprene and 1,3-butadiene with a vinyl aromatic compound selected from styrene and alpha methylstyrene, (B) about 10 to about 150 phr of at least one particulate reinforcing filler comprised of about 10 to about 100 phr of at least one particulate synthetic silica-based material having hydroxyl groups on the surface thereof selected from at least one of aggregates of synthetic amorphous silica, fumed silica, and silica modified carbon black, and correspondingly, from zero to about 80 phr of rubber reinforcing carbon black, and (C) at least one organo-metal compound as an organo-tin compound selected from the group consisting of dibutyltin dilaurate, di-n-butylbis(2-ethylhexanoate)tin, di-n-butylbis(2,4-pentanedionate)tin, di-n-butyldiacetoxytin, di-n-butyldiacrylatetin, di-n-butyldimethacrylatetin, dimethyldineodecanoatetin, dioctyldilauryltin and dioctyldineodecanoatetin.
United States Patent Application Publication No. 2006/0169391 A1 discloses a method for preparing a tire comprising the steps of: mixing ingredients including silica and at least one elastomer to form a first mixture, where the elastomer optionally includes silica-reactive functionalized elastomer; cooling the first mixture; further mixing the first mixture, optionally with additional ingredients including a silica coupling agent, a silica reactive dispersing agent or both, to form an intermediate mixture, with the proviso that at least one of the ingredients mixed to form the first mixture or the additional ingredients added to form the intermediate composition includes a silica-reactive compound; adding ingredients including a curative to the intermediate mixture to form a vulcanizable mixture; mixing the vulcanizable mixture; forming the vulcanizable mixture into a tire component; building a tire by including the tire component; curing the tire; where a titanium compound is added to at least one of said step of mixing ingredients to form a first mixture or said step of further mixing to form an intermediate mixture.
The importance of attaining good to compatibility between rubbers and fillers used in tires and other industrial products is well appreciated. For example, in tire tread compounds improved compatibility between the rubber and the filler, such as carbon black or silica, normally results in lower hysteresis and improved tire tread life. Low hysteresis in tire tread compounds is desirable because it is indicative of lower heat generation during rolling and lower rolling resistance which leads to better fuel economy. U.S. Pat. No. 7,108,033 discloses rubber compositions that attain improved compatibility with the types of fillers that are typically used in rubber compounds, such as carbon black and silica, through the utilization of rubbery polymers that contain repeat units that are derived from one or more conjugated diolefin monomers and at least one monomer that is functionalized with a leaving group, such as a halogen.
U.S. Pat. Nos. 6,693,160, 6,753,447 6,812,307, 6,825,306, 6,901,982, 6,933,358, 6,936,669, 7,041,761, 6,627,721, 6,627,722, 6,630,552, 6,664,328, 6,790,921, and 6,927,269 disclose the incorporation of functionalized monomers into rubbery polymers to improve compatibility with fillers.